Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1998-04-29
2000-05-16
Niland, Patrick D.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524591, 524839, 524840, 528 45, C08J 300, C08K 320, C08L 7500, C08G 1800, C08G 1881
Patent
active
060638605
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to water dispersible blocked polyisocyanates, methods for making them, water-based storage stable materials, and coatings containing them.
Blocked polyisocyanates are commonly used in coatings, such as paints, which also contain active hydrogen containing compounds e.g. amines and alcohols. These coatings are deposited onto the article to be coated and then subsequently hardened by heating, often referred to as stoving. During stoving the blocked polyisocyanates dissociate so that the isocyanate groups become available to react with the active hydrogen containing compounds. This leads to crosslinking and hardening of the coating.
A blocked polyisocyanate coating composition ideally has two properties: (a) a dissociation temperature low enough to allow hardening without heating to temperatures which degrade the coated item and (b) water dispersibility so that the use of organic solvents can be kept to a minimum or eliminated. However, generally a blocked polyisocyanate having a low dissociation temperature will be highly reactive and thus will be inherently unstable in water so that the two properties are incompatible.
Various means for increasing water dispersibility have been described.
U.S. Pat. No. 4,522,851 describes a water-dispersible blocked isocyanate in which a hydrophilic group such as an anionic group is chemically incorporated into the polyisocyanate component to make the blocked polyisocyanate water-dispersible. U.S. Pat. No. 4,507,427 describes aqueous blocked polyisocyanate solutions or dispersions produced by mixing the blocked polyisocyanate with water in the presence of enough base to guarantee the solubility or dispersibility of the polyisocyanates. U.S. Pat. No. 4,098,933 describes water-dispersible blocked polyisocyanates in which the blocking groups contain a hydrophilic group such as a carboxylic acid salt or polyethylene oxide units.
Most conventional blocked polyisocyanates dissociate at temperatures of around 160.degree. C. EP-A-0159117 discloses pyrazole blocked polyisocyanates which dissociate at a temperature significantly lower than this. Since the pyrazole blocked polyisocyanates are more reactive than conventional blocked isocyanates, they are inherently less stable.
The present inventors have now established that, despite their high reactivity, certain pyrazole blocked polyisocyanates can be used in aqueous dispersion coating compositions and that the compositions have good storage stability. Accordingly the present invention provides a water dispersible blocked polyisocyanate of the formula (I) heterocyclic or aromatic group and comprising at least three consecutive ethylene oxide groups or at least one residue of a polyhydroxy carboxylic acid, (II) ##STR2## where R.sup.1 is an alkyl, alkenyl, aralkyl, N-substituted carbamyl, phenyl, NO.sub.2, halogen or a group --C(O)--O--R.sup.2 where R.sup.2 is hydrogen or an alkyl group;
Preferably m is an integer from 2 to 6, for example 2, 3, 4, 5 or 6. When n is 2 or 3, the groups R.sub.1 may be the same or different. When R--Y.sub.m contains more than one group --C(O)OR.sup.2, the groups R.sup.2 may be the same or different.
In addition the present invention provides a water dispersible mixture of blocked polyisocyanates each of the formula comprising an aliphatic, cycloaliphatic heterocyclic or aromatic group and wherein from 5 to 100 eq.wt % (preferably from 10 to 100 eq.wt %) of groups R comprise at least three consecutive ethylene oxide groups or at least one residue of a polyhydroxy carboxylic acid, (II) as defined above.
According to a further embodiment, the invention provides a water dispersible product obtainable by heterocyclic or aromatic group and which is --(CH.sub.2 CH.sub.2 O).sub.p -- where p is 3 or more or with a polyhydroxy carboxylic acid group or derivative thereof to form a water dispersible polyisocyanate of formula R(NCO).sub.m where R is an m valent group comprising an aliphatic, cycloaliphatic, heterocyclic or aromatic group comprising at least three consecutive ethylene oxide
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Rimmer Ian Kevin
Spencer Richard Alan
Baxenden Chemicals Limited
Niland Patrick D.
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